Wearable eButton for Evaluation of Energy Balance with Environmental Context and Behavior Overweight and obesity have become a wide spread epidemic affecting more than 60% of the population in the United States. A recent study indicates that the estimated direct and indirect costs of obesity to the U.S. economy are at least $215 billion annually. In the battle against obesity and related diseases, both the research and clinical communities require an accurate tool to measure people's energy intake and expenditure in real life. However, presently, the most utilized tool is still a questionnaire which is subjective and often inaccurate. The current state-of-the-art in diet and physical activity measurement has fallen far behind what the modern technology is able to provide. The field is mature for a substantial innovation. In this application, we propose the development of a new electronic device which has the potential to produce a technological quantum leap in the measurement of diet and physical activity. This button- like device, eButton, will be worn naturally on the chest using a pair of magnets or a pin. A new measurement concept based on the use of the wearable computer will be utilized in our device design. The eButton will contain a low-power, high-performance microprocessor running a simplified version of the LINUX operating system. It will contain numerous innovative designs, including an optical eating detector to monitor eating/drinking/smoking, two miniature cameras that produce a stereo vision to measure food portion size without depending on a reference card, an ear-based oximeter for measurement of heart rate and oxygen saturation, and an extrapolation formula to measure outdoor environment using the US environmental protection agency (EPA) database. eButton will store the multimedia data acquired by a variety of advanced miniature sensors in a flash memory within the device. It will also have a wireless link to a smart phone which will allow researchers to monitor the operating status of eButton remotely in real time. All sensors and function modules will be individually controlled by software to allow researchers to select among the available system resources for their particular needs. Despite the wide functionality of the device, eButton requires an extremely low user respondent burden. The research participant is required to do nothing more than turning on/off the device and recharging its battery at night. During our research, eButton and associated algorithms/software will be designed and constructed in our laboratory by an experienced team of electronic/software engineers based on an early version of the device developed under the NIH GEI diet and physical activity research program. Once eButton is constructed, we will implement a thorough validation process using human subjects to evaluate its accuracy in diet and physical activity assessment by comparing against the doubly-labeled water method as the gold standard.